Photoresist stripping solution and a method of stripping photoresists using the same

ABSTRACT

A photoresist stripping solution which comprises (a) a salt of hydrofluoric acid with a base free from metal ions, (b) a water-soluble organic solvent, (c) a mercapto group containing corrosion inhibitor, and (d) water, and a method of stripping photoresists with the use of the same are disclosed. In case of using ammonium fluoride as component (a), the photoresist stripping solution may further contain (e) a salt of hydrofluoric acid with a quaternary ammonium hydroxide, such as tetramethylammonium hydroxide, tetrapropylammonium hydroxide, etc., and/or an alkanolamine. The photoresist stripping solution of the present invention has an excellent effect of protecting both Al- and Cu-based metal wiring conductors from corrosion, of efficiently stripping photoresist films and post-ashing residues, and is free from the precipitation of the corrosion inhibitor.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a photoresist stripping solution and a methodof stripping photoresists using the same. More particularly, it relatesto a photoresist stripping solution which is excellent in protectingboth Al- and Cu-based wiring conductors and other metal conductors fromcorrosion and in stripping photoresist films and post-ashing residues;and a method of photoresists using the same. The present invention issuitable for use in the fabrication of semiconductor devices such as ICsand LSIs, as well as liquid-crystal panel apparatus.

2. Description of Relevant Art

The fabrication of semiconductor devices such as ICs and LSIs, as wellas liquid-crystal panel apparatus, comprises forming a uniformphotoresist coating over conductive metallic layers, insulation layerssuch as an SiO₂ film formed on a substrate (silicon wafer) by CVD;performing selective exposure and development to form a photoresistpattern; selectively etching the substrate having the conductivemetallic layers, the insulation layers formed thereon using thephotoresist pattern as a mask to thereby form a microcircuit; and thenremoving the unwanted photoresist layer with a stripping solution. Forremoval of such unwanted photoresist layers, various organic strippingsolutions has been used from safety and strippability standpoints.

Examples of the conductive metallic layers formed by CVD as describedabove include those of aluminum (Al); aluminum alloys (Al alloys) suchas aluminum-silicon (Al—Si), aluminum copper (Al—Cu) andaluminum-silicon-copper (Al—Si—Cu); titanium (Ti); titanium alloys (Tialloys) such as titanium nitride (TiN) and titanium-tungsten (TiW);tantalum (Ta), tantalum nitride (TaN), tungsten (W), tungsten nitride(WN) and copper (Cu). These conductive metallic films are formed in oneor more layers on the substrate. In recent years, both of devices havingAl-based conductors (Al and Al alloy-based wirings) and devices havingCu-based conductors are coexisted. Accordingly, it has been required toprotect both of these two types of devices from corrosion with the useof a single photoresist stripping solution.

Furthermore, with the recent tendency toward highly integrated,high-density circuits, dry etching enabling fine etching with a higherdensity has become the major means. Also, it has been a practice toemploy plasma ashing to remove the unwanted photoresist layers remainingafter etching. After these etching and ashing treatments, residuescomprising modified photoresist films and other components that arereferred to horn-like shaped “veil”, “fences” or “side-walls” remain onthe bottom or side wall of patterned grooves. In case of forming apattern on a substrate having an Si-based interlayer film, such as anSi-based insulation film (SiN film, SiO₂film, etc.) and a low dielectricfilm (SOG film, etc.), Si-based residues (Si-based depositions) aresometimes formed around pattern hole openings. In addition, etching ofmetallic layers and ashing treatment builds up metal depositions. Suchpost-ashing residues or depositions should be completely stripped awayso as to keep good yields in the fabrication of semiconductors.

In recent years, further highly-density and highly-integrated substratesare needed, and thus the treating conditions in the etching and ashingsteps become more and more strict. As a result, it is also urgentlyrequired to achieve improved corrosion resistance of metal wirings aswell as improved residue-strippability of stripping solutions, comparedwith conventional ones.

Under these circumstances, there have been frequently employed strippingsolutions for photoresists and post-ashing residues which contain aminesor hydrofluoric acid as the main component. Among all, those containinghydrofluoric acid as the main component show excellent strippabilityespecially for post-ashing residues.

Examples of stripping solutions containing hydrofluoric acid as the maincomponent include: a resist stripping solution composition of pH 5-8containing a salt of hydrofluoric acid with a base free from metal ions,a water-soluble organic solvent and water optionally together with acorrosion inhibitor (JP-A-9-197681); and a cleaner for semiconductordevices containing a quaternary ammonium salt and a fluorine compound,and further adding a water-soluble organic solvent (JP-A-7-201794).

The resist stripping solution composition in JP-A-9-197681 is to acertain extent effective in strippability and anti-corrosivity onsemiconductor devices having Al wiring conductors, however, it fails toexert any satisfactory effect of protecting devices having Cu wiringconductors from corrosion.

In the cleaner in JP-A-7-201794, tetramethylammonium formate andtrimethyl(2-hydroxyethyl)ammonium salt are used as the quaternaryammonium salt. Although the corrosion of Cu wiring conductors can berelieved to a certain extent by using these compounds, there arisesanother problem that strippability for Cu-based metallic depositions(residues) is still insufficient.

JP-A-2000-273666 teaches a cleaner solution containing a sulfur-basedcorrosion inhibitor for protecting Cu wiring conductors from corrosion.However, any satisfactory strippability for Cu-based metallicdepositions (residues) also cannot be established by using this cleanersolution.

As discussed above, none of the conventional photoresist strippingsolutions can satisfy both of the requirements for efficientstrippability and effective inhibition of metal corrosion. This isbecause strippability offsets the performance of inhibiting corrosion ina photoresist stripping solution. That is to say, there is a problemthat one of the above-described requirement cannot be fulfilled unlessthe other is sacrificed. In the ultrafine processing employed in thesedays, in particular, the strippability for photoresist films andpost-ashing residues should be further improved and it is thereforeneeded to enhance the effect of protecting metal wirings from corrosion.Recent models of semiconductor devices can be divided into two type, oneusing Al wiring conductors (Al, Al alloy and other Al-based metalwiring) and the other using Cu wiring conductors (Cu-based metalwiring). In addition to the need to protect devices of these two typesfrom corrosion with the use of a single stripping solution, it is alsorequired to provide effective protection against corrosion of othermetals on the devices. Further improvements are desired to achieveeffective stripping away of photoresists and post-ashing residues and toprotect metal conductors from corrosion.

SUMMARY OF THE INVENTION

The present invention has been accomplished under these circumstancesand has as an object of providing a photoresist stripping solution thatis suitable for use in the photolith-graphic technology to form today'ssemiconductor and liquid-crystal display devices having an everdecreasing feature size and an increasing number of interlevel filmssuperposed on the substrate, and that can assure effective protection ofAl, Cu and other wiring metal conductors against corrosion as well asefficient stripping of the photoresist film and post-ashing residues.

To attain the above-described objects, the present invention provides aphotoresist stripping solution which comprises (a) a salt ofhydrofluoric acid with a base free from metal ions, (b) a water-solubleorganic solvent, (c) a mercapto group containing corrosion inhibitor,and (d) water.

The present invention also provides a photoresist stripping solutionwhich further contains, in addition to components (a)-(d), with theproviso that component (a) is ammonium fluoride, (e) a salt ofhydrofluoric acid with a quaternary ammonium hydroxide represented bythe following general formula (I) and/or an alkanolamine:

wherein R₁, R₂, R₃ and R₄ are each independently an alkyl group or ahydroxyalkyl group having 1 to 4 carbon atoms.

The present invention furthermore provides a method of strippingphotoresists which comprises forming a photoresist pattern on asubstrate, etching the substrate using the photoresist as a mask, andthereafter stripping away the photoresist pattern from the substrateusing the photoresist stripping solution as described above.

The present invention still furthermore provides a method of strippingphotoresists which comprises forming a photoresist pattern on asubstrate, etching the substrate using the photoresist as a mask, thenplasma ashing the photoresist pattern, and thereafter stripping awaypost-plasma ashing residues from the substrate using the photoresiststripping solution as described above.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will be described below in detail.

In the present invention, component (a) is a salt of hydrofluoric acidwith a base free from metal ions. Preferable examples of the base freefrom metal ions include hydroxylamines, organic amines such as primary,secondary or tertiary aliphatic amines, alicyclic amines, aromaticamines and heterocyclic amines, aqueous ammonia, and lower alkylquaternary ammonium hydroxides.

Specific examples of the hydroxylamines include hydroxylamine (NH₂OH),N-methylhydroxylamine, N,N-dimethylhydroxylamine andN,N-diethylhydroxylamine.

Specific examples of the primary aliphatic amines includemonoethanolamine, ethylenediamine and 2-(2-aminoethylamino)ethanol.

Specific examples of the secondary aliphatic amines includediethanolamine, N-methylaminoethanol, dipropylamine and2-ethylaminoethanol.

Specific examples of the tertiary aliphatic amines includedimethylaminoethanol and ethyldiethanolamine.

Specific examples of the alicyclic amines include cyclohexylamine anddicyclohexylamine.

Specific examples of the aromatic amines include benzylamine,dibenzylamine and N-methylbenzylamine.

Specific examples of the heterocyclic amines include pyrrole,pyrrolidine, pyrrolidone, pyridine, morpholine, pyrazine, piperidine,N-hydroxyethylpiperidine, oxazole and thiazole.

Specific examples of the lower alkyl quaternary ammonium salts includetetramethylammonium hydroxide (TMAH), tetraethylammonium hydroxide,tetrapropylammonium hydroxide, trimethylethylammonium hydroxide,(2-hydroxyethyl)trimethylammonium hydroxide,(2-hydroxyethyl)triethylammonium hydroxide,(2-hydroxyethyl)tripropylammonium hydroxide and(1-hydroxypropyl)trimethylammonium hydroxide.

Among these bases, aqueous ammonia, monoethanolamine,N-methylaminoethanol, tetramethylammonium hydroxide and(2-hydroxyethyl)trimethylammonium hydroxide are preferable fromavailability and safety standpoints.

The bases free from metal ions may be used either alone or incombination with one another.

The salt of hydrofluoric acid with the base free from metal ions may beprepared using a commercially available hydrofluoric acid having aconcentration of 50-60% and adding thereto the base free from metalions. As the salt, ammonium fluoride (NH₄F) may be the most desirable.Either one or more salts may be used as component (a).

The content of component (a) preferably ranges 0.1-10 mass percent,still preferably 0.2-3 mass percent in the stripping solution of theinvention. In case where the content of component (a) is too large, Cuwiring conductors tend to corrode. In case where its content is toosmall, on the other hand, the strippability is liable to be lowered.

As component (b) that is a water-soluble organic solvent, use may bemade of those commonly employed in the art. Such a water-soluble organicsolvent is not specifically restricted so long as it is miscible withwater and other components employed in the present invention. Specificexamples thereof include: sulfoxides, such as dimethyl sulfoxide;sulfones, such as dimethyl sulfone, diethyl sulfone,bis(2-hydroxyethyl)sulfone and tetramethylene sulfone; amides, such asN,N-dimethylformamide, N-methylformamide, N,N-dimethylacetamide,N-methylacetamide and N,N-diethylacetamide; lactams, such asN-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone, N-propyl-2-pyrrolidone,N-hydroxymethyl-2-pyrrolidone and N-hydroxyethyl-2-pyrrolidone;imidazolidinones, such as 1,3-dimethyl-2-imidazolidinone,1,3-diethyl-2-imidazolidinone and 1,3-diisopropyl-2-imidazolidinone; andpolyhydric alcohols and derivatives thereof, such as ethylene glycol,ethylene glycol monomethyl ether, ethylene glycol monoethyl ether,ethylene glycol monobutyl ether, ethylene glycol monomethyl etheracetate, ethylene glycol monoethyl ether acetate, diethylene glycol,diethylene glycol monomethyl ether, diethylene glycol monoethyl ether,diethylene glycol monobutyl ether, propylene glycol monomethyl ether,propylene glycol monoethyl ether, propylene glycol monopropyl ether andpropylene glycol monobutyl ether. Among these organic solvents,preferable ones are dimethylformamide, N-methyl-2-pyrrolidone anddimethyl sulfoxide. Dimethylformamide is the most desirable since it canbe easily handled after stripping treatment. Either one or more solventsmay be used as component (b).

The content of component (b) preferably ranges 30-80 mass percent, stillpreferably 40-75 mass percent in the stripping solution of the presentinvention. In case where the content of component (b) is too large, thestrippability is liable to be lowered. In case where its content is toosmall, on the other hand, various metal wiring conductors tend tocorrode.

Although the mercapto group containing corrosion inhibitor to be used ascomponent (c) is not specifically restricted so long as it can protectmetal atoms employed in wiring conductors (in particular, Al wiring orCu wiring) from corrosion, it is preferable to use a compound having inits structure a hydroxyl group and/or a carboxyl group at least one ofthe α- and β-positions. Specific examples of such a compound include1-thioglycerol, 3-(2-aminophenylthio)-2-hydroxypropylmercaptan,3-(2-hydroxyethylthio)-2-hydroxypropylmercaptan, 2-mercaptopropionicacid and 3-mercaptopropionic acid. Among these compounds, 1-thioglycerolis particularly preferable. In the present invention, component (c) isused as a corrosion inhibitor to thereby achieve an excellent effect ofprotecting Al and Cu wiring conductors from corrosion as well as aneffect of preventing precipitation of the corrosion inhibitor.

Either one or more compounds may be used as component (c). The contentof component (c) preferably ranges 0.1-10 mass percent, still preferably0.2-5 mass percent in the stripping solution of the invention. In casewhere the content of component (a) is too small, there is a fear thatinsufficient effect may be provided for protecting in particular Cuwiring conductors from corrosion.

Component (d) in the stripping solution of the invention is water.Although some water is contained inevitably in other components, wateris intentionally added to adjust the content. The content of component(d) is the balance of the stripping solution of the present invention.

In addition to components (a)-(d), with the proviso that component (a)is ammonium fluoride, the stripping solution of the invention mayfurther incorporate into the stripping solution (e) a salt ofhydrofluoric acid with a quaternary ammonium hydroxide represented bythe following general formula (I) and/or an alkanolamine:

wherein R₁, R₂, R₃ and R₄ are each independently an alkyl group or ahydroxyalkyl group having 1 to 4 carbon atoms. Use of component (e)contributes to the improvement in the strippability without seriouslydamaging Cu.

Specific examples of the quaternary ammonium hydroxide represented bythe general formula (I) include tetramethylammonium hydroxide (TMAH),tetraethylammonium hydroxide, tetrapropylammonium hydroxide,tetrabutylammonium hydroxide, monomethyltripleammonium hydroxide,trimethylethylammonium hydroxide, (2-hydroxyethyl)trimethylammoniumhydroxide, (2-hydroxyethyl)triethylammonium hydroxide,(2-hydroxyethyl)tripropylammonium hydroxide and(1-hydroxypropyl)trimethylammonium hydroxide. Among these compounds,TMAH, tetraethylammonium hydroxide, tetrapropylammonium hydroxide,tetrabutylammonium hydroxide, monomethyltripleammoniumhydroxide,(2-hydroxyethyl)trimethylammoniumhydroxide, etc. are preferable fromavailability and safety standpoints.

Examples of the above-described alkanolamines include monoethanolamine,diethanolamine, triethanolamine, 2-(2-aminoethoxy)ethanol,N,N-dimethylethanolamine, N,N-diethylethanolamine,N,N-dibutylethanolamine, N-methylethanolamine, N-ethylethanolamine,N-butylethanolamine, N-methyldiethanolamine, monoisopropanolamine,diisopropanolamine and truisopropanolamine. Among these compounds,N-methylethanolamine is particularly preferable in terms of protectingCu wiring conductors from corrosion.

Either one or more compounds may be used as component (e). The contentof component (e) preferably ranges 0.1-10 mass percent, still preferably0.2-3 mass percent in the stripping solution of the invention. In casewhere the content of component (e) is too large, Al wiring conductorstend to corrode.

In case of using component (e) in the present invention, it ispreferable to adjust the composition ratio of ammonium fluoride employedas component (a) to component (e) [ammonium fluoride : component (e)] tofrom 2:8 to 8:2 by mass, still preferably from 3:7 to 7:3. By regulatingthe composition ratio of fluoride ammonium to component (e) within therange as specified above, metal wiring conductors can be moreefficiently protected from corrosion. In case where the content ofammonium fluoride exceeds the upper limit as specified above, Al-basedwiring conductors are prone to corrode. In case where the content ofcomponent (e) exceeds the upper limit as specified above, on the otherhand, Cu-based wiring conductors are prone to corrode.

In order to improve penetrating properties, the stripping solution ofthe invention may further contain, as an optional component, anacetylene alcohol/alkylene oxide adduct prepared by adding an alkyleneoxide to an acetylene alcohol.

As the acetylene alcohol as described above, use may be preferably madeof compounds represented by the following general formula (II):

wherein R₅ is a hydrogen atom or a group represented by the followingformula (III);

and R₆, R₇, R₈ and R₉ are each independently a hydrogen atom or an alkylgroup having 1-6 carbon atoms.

These acetylene alcohols are commercially available under trade names of“Surfynol” and “Olfin” series (both are produced by Air Products andChemicals Inc.). Among these commercial products, “Surfynol 104”,“Surfynol 82” or mixtures thereof are most preferred for the physicalproperties. Use can be also made of “Olfin B”, “Olfin P”, “Olfin Y” etc.

As the alkylene oxide to be added to the acetylene alcohol as describedabove, it is preferred to use ethylene oxide, propylene oxide or amixture thereof.

In the present invention, it is preferable to use, as the acetylenealcohol/alkylene oxide adduct, compounds represented by the followinggeneral formula (IV):

wherein R₁₀ is a hydrogen atom or a group represented by the followingformula (V):

and R₁₁, R₁₂, R₁₃ and R₁₄ are each independently a hydrogen atom or analkyl group having 1-6 carbon atoms; (n+m) is an integer of 1 to 30,which is the number of ethylene oxide molecules added. This numbersubtly affects the properties of the compound such as water solubilityand surface tension.

The acetylene alcohol/alkylene oxide adducts per se are known assurfactants. These products are commercially available under the tradename “Surfynol” series (products of Air Product and Chemicals Inc.) and“Acetylenol” series (products of Kawaken Fine Chemicals Co., Ltd.) andhave been appropriately utilized. Among these products, it is preferredto use “Surfynol 440” (n+m=3.5), “Surfynol 465” (n+m=10), “Surfynol 485”(n+m=30), “Acetylenol EL” (n+m=4), “Acetylenol EH” (n+m=10) or mixturesthereof, in view of the changes in their physical properties such aswater solubility and surface tension depending on the number of ethyleneoxide molecules added. A mixture of “Acetylenol EL” with “Acetylenol EH”in a mass ratio of 2:8 to 4:6 is particularly desirable.

Use of the acetylene alcohol/alkylene oxide adduct makes it possible toimprove the penetrating properties and wetting properties of thestripping solution.

When the stripping solution of the invention contains the acetylenealcohol/alkylene oxide adduct, the content thereof is preferably 0.05-5mass percent, more preferably 0.1-2 mass percent. When the contentexceeds the upper limit as defined above, it tends to cause foaming butthe wetting properties cannot be improved any more. When the content isless than the lower limit as defined above, on the other hand, thedesired improvement in the wetting properties can be scarcely obtained.

To complete the stripping treatment in a short period of time, thestripping solution of the invention may further contain an acidiccompound. Examples of the acidic compound include hydrofluoric acid,acetic acid and glycolic acid. In case of using such an acidic compound,its content is preferably 1 mass percent or less. When the strippingsolution of the invention contains the acidic compound, thestrippability of Si-based depositions can be particularly improved.Thus, the stripping time can be shortened and an excellent effect ofstripping Si-based depositions can be established thereby.

The photoresist stripping solution of the invention can advantageouslybe used with all photoresists, whether negative- or positive-working,that can be developed with aqueous alkaline solutions. Such photoresistsinclude, but are not limited to, (i) a positive-working photoresistcontaining a naphthoquinonediazide compound and a novolak resin, (ii) apositive-working photoresist containing a compound that generates anacid upon exposure, a compound that decomposes with an acid to have ahigher solubility in aqueous alkali solutions, and an alkali-solubleresin, (iii) a positive-working photoresist containing a compound thatgenerates an acid upon exposure and an alkali-soluble resin having agroup that decomposes with an acid to have a higher solubility inaqueous alkali solutions, and (iv) a negative-working photoresistcontaining a compound that generates an acid upon illumination withlight, a crosslinker and an alkali-soluble resin.

According to the invention, photoresists are stripped away by one of twomethods which have the following steps in common: forming a photoresistpattern by lithography on a substrate having conductive metallic layers,insulation layers and low-dielectric layers thereon, and selectivelyetching the layers with the photoresist pattern used as a mask to form afine-line circuit. After these steps, the photoresist pattern isimmediately stripped away (method I), or the etched photoresist patternis subjected to plasma ashing and thereby post-ashing residues, such asthe modified photoresist film (photoresist film residue) and metaldeposition, are stripped away (method II).

An example of method I in which the photoresist film is stripped awayimmediately after etching comprises:

-   -   (I) providing a photoresist layer on a substrate;    -   (II) selectively exposing said photoresist layer;    -   (III) developing the exposed photoresist layer to provide a        photoresist pattern;    -   (IV) etching the substrate to form a pattern using said        photoresist pattern as a mask; and    -   (V) stripping away the photoresist pattern from the etched        substrate using the photoresist stripping solution of the        present invention.

An example of method II in which the modified photoresist film and metaldeposition resulting from plasma ashing are stripped away after etchingcomprises:

-   -   (I) providing a photoresist layer on a substrate;    -   (II) selectively exposing said photoresist layer;    -   (III) developing the exposed photoresist layer to provide a        photoresist pattern;    -   (IV) etching the substrate to form a pattern using said        photoresist pattern as a mask;    -   (V) plasma ashing the photoresist pattern;    -   (VI) stripping away the post-ashing residues using the        photoresist stripping solution of the present invention.

The specific advantage of the present invention resides in that thephotoresist stripping solution has excellent effects of strippingphotoresist films and post-ashing residues (modified photoresist films,metal depositions, etc.) and protecting a substrate having metalconductors from corrosion both in stripping away photoresists formed ona substrate having Al wiring conductors and formed on a substrate havingCu wiring conductors.

Examples of the metal wiring conductors include, but are not limited to,those made of aluminum (Al); aluminum alloys such as aluminum copper(Al—Cu) and aluminum-silicon-copper (Al—Si—Cu); titanium (Ti); titaniumalloys (Ti alloys) such as titanium nitride (TiN) and titanium-tungsten(TiW); and copper (Cu).

Using conventional photoresist stripping solutions, it is very difficultto satisfy both of the requirements for efficient strippability forphotoresists and post-ashing residues and effective inhibition of metalcorrosion in Al-based wiring devices and Cu-based wiring devices.According to the present invention, however, both of these requirementscan be successfully satisfied by combining components (a)-(d)with eachother. Using component (e) in addition to components (a)-(d), with theproviso that component (a) is ammonium fluoride, the strippability canbe further improved without seriously damaging Cu.

In the second stripping method described above, residue adhere to thesubstrate surface after plasma ashing, such as photoresist residue(modified photoresist film) and metal deposition that formed duringetching of the metal film. These residues are contacted by the strippingsolution of the invention so that they are stripped away from thesubstrate surface. Plasma ashing is inherently a method for removing thephotoresist pattern but it often occurs that part of the photoresistpattern remains as a modified film; the present invention isparticularly effective for the purpose of completely stripping away suchmodified photoresist film.

In forming the photoresist layer, and exposing, developing and etchingtreatments, any conventional means may be employed without particularlimitation.

After the development step (III) or the stripping step (V) or (VI),conventional rinsing may optionally be performed using pure water, loweralcohols, etc., followed by drying.

The photoresist is usually stripped by the dip, shower or paddle method.The stripping time is not limited to any duration as long as it issufficient to achieve removal of the photoresist.

EXAMPLES

The following examples are provided for the purpose of furtherillustrating the present invention but are in no way to be taken aslimiting. Unless otherwise noted, all compounding amounts are expressedby mass percent.

[Treatment 1]

A silicon wafer having an SiO₂ layer formed thereon was used as asubstrate. On this substrate, a TiN layer, an Al—Si—Cu layer and anotherTiN layer were successively formed thereon respectively as the first,second and third layers. The topmost layer was spin-coated with apositive-working photoresist (TDUR-P015 of Tokyo Ohka Kogyo Co., Ltd.),which was prebaked at 80° C. for 90 seconds to form a photoresist layer0.7 μm thick.

The photoresist layer was exposed through a mask pattern using FPA 3000EX3 (Canon Inc.), then subjected to post-exposure bake at 110° C for 90seconds and developed with an aqueous solution of 2.38 mass percenttetraammonium hydroxide (TMAH) to form a photoresist pattern of 400 nmin line-and-space. Subsequently it was subjected to dry etching andplasma ashing.

[Treatment II]

A silicon wafer having Cu layer that is overlaid with an SiO₂ layerformed by plasma CVD was used as a substrate. The substrate wasspin-coated with a positive-working photoresist (TDUR-P015 of Tokyo OhkaKogyo Co., Ltd.), which was prebaked at 80° C. for 90 seconds to form aphotoresist layer 0.7 μm thick.

The photoresist layer was exposed through a mask pattern using FPA 3000EX3 (Canon Inc.), then subjected to post-exposure bake at 110° C. for 90seconds and developed with an aqueous solution of 2.38 mass percenttetraammonium hydroxide (TMAH) to form a hole pattern of 200 nm indiameter. Subsequently it was subjected to dry etching and plasmaashing.

Examples 1-8 and Comparative Examples 1-5

The thusly treated substrate in treatment I or II as described above wasdipped (25° C., 5 minutes) in each photoresist stripping solution asindicated in Table 1 for stripping. In Example 8, dipping was carriedout for 1 minute. After the completion of the stripping treatment, eachsubstrate was rinsed with purified water. Then the substrate wasobserved under a scanning electron microscope (SEM) to evaluatestrippability of the post-ashing residues, state of corrosion of metalwiring conductors and precipitation of the corrosion inhibitor. Theresults are shown in Table 2.

The strippability of the post-ashing residues, state of corrosion ofmetal wiring conductors and precipitation of the corrosion inhibitorwere evaluated in accordance with the following criteria.

The strippability of the post-ashing residues was evaluated by using thesubstrate treated in treatment II. Regarding the protection of metalsfrom corrosion, the substrate treated in treatment I was mainly used forAl wiring, and the one treated in treatment II was mainly used for Cuwiring. The precipitation of the corrosion inhibitor was evaluated byusing the substrate treated in treatment II.

[Strippability of Post-Ashing Residues (Cu-Based Depositions andSi-Based Depositions)]

⊚: Complete stripping

◯: Almost complete stripping

Δ: Some residues remained

×: Much residues remained

[Protection of Metal Wiring Conductors (Al and Cu) from Corrosion]

⊚: No corrosion found

◯: Little corrosion found

Δ: Suffered from somewhat corrosion

×: Suffered from corrosion

[State of Precipitation of Corrosion Inhibitor]

⊚: No precipitation of corrosion inhibitor found

◯: Little precipitation of corrosion inhibitor found

Δ: Suffered from somewhat precipitation of corrosion inhibitor

×: Suffered from precipitation of corrosion inhibitor TABLE 1Photoresist stripping solution (mass %) Component Component ComponentComponent Other (a) (b) Component (c) (d) (e) component Ex. 1 NH₄F DMSOCor. inhib. A water — — (0.5) (70) (2) (27.5) Ex. 2 NH₄F DMSO Cor.inhib. B water — — (2) (50) (1) (47) Ex. 3 NH₄F DMF Cor. inhib. C water— acetylene (1) (60) (1) (37.5) alcohol/ alkylene oxide adduct (0.5) Ex.4 NH₄F DMSO Cor. inhib. D water HF/TMAH — (0.5) (70) (1) (28) (0.5) Ex.5 NH₄F DMSO Cor. inhib. E water HF/TPAH acetylene (1.2) (50) (0.5)(45.5) (1.8) alcohol/ alkylene oxide adduct (1) Ex. 6 NH₄F DMF Cor.inhib. A water HF/TMAH — (0.6) (70) (1) (28) (0.4) Ex. 7 NH₄F NMP Cor.inhib. A water HF/TMAH — (0.4) (70) (1) (28) (0.6) Ex. 8 NH₄F NMP Cor.inhib. A water HF/TMAH acetic (0.5) (70) (1) (27.7) (0.5) acid(0.3) Com.NH₄F DMSO Cor. inhib. X water — — Ex. 1 (2) (60) (2) (36) Com. NH₄F DMSOCor. inhib. Y water — — Ex. 2 (1) (50) (1) (48) Com. NH₄F DMSO Cor.inhib. Z water — — Ex. 3 (0.5) (75) (2) (22.5) Com. NH₄F DMSO Cor.inhib. X water HF/TMAH — Ex. 4 (0.5) (70) (1) (28) (0.5) Com. NH₄F DMSOCor. inhib. X water HF/TPAH — Ex. 5 (2) (50) (0.5) (46.5) (1)

The symbols used in Table 1 to indicate respective components have thefollowing definitions.

NH₄F: ammonium fluoride

DMSO: dimethyl sulfoxide

DMF: dimethylformamide

NMP: N-methyl-2-pyrrolidone

Cor. inhib. A: 1-thioglycerol

Cor. inhib. B: 3-(2-aminophenylthio)-2-hydroxypropylmercaptan

Cor. inhib. C: 3-(2-hydroxyethylthio)-2-hydroxypropylmercaptan

Cor. inhib. D: 2-mercaptopropionic acid

Cor. inhib. E: 3-mercaptopropionic acid

Cor. inhib. X:2,2′-{[(4-methyl-1H-benzo-triazol-1-yl)methyl]imino}-bisethanol(“IRGAMET 42”)

Cor. inhib. Y: pyrogallol

Cor. inhib. Z: pyrocatechol

HF/TMAH: salt of hydrofluoric acid (HF) with tetramethyl-ammoniumhydroxide (TMAH)

HF/TPAH: salt of hydrofluoric acid (HF) with tetrapropyl-ammoniumhydroxide (TPAH) TABLE 2 Protection of Strippability of metal conductorPrecipitation post-ashing residues from corrosion of Cu-based Si-basedCu Al corrosion deposition deposition wiring wiring inhibitor Ex. 1 ◯ ◯◯ ◯ ◯ Ex. 2 ◯ ◯ ◯ ◯ ◯ Ex. 3 ◯ ◯ ◯ ◯ ◯ Ex. 4 ◯ ◯ ⊚ ◯ ◯ Ex. 5 ◯ ◯ ⊚ ◯ ◯Ex. 6 ◯ ◯ ⊚ ◯ ◯ Ex. 7 ◯ ◯ ⊚ ◯ ◯ Ex. 8 ◯ ⊚ ⊚ ◯ ◯ Com. Ex. 1 ◯ ◯ Δ ◯ XCom. Ex. 2 ◯ ◯ X ◯ ◯ Com. Ex. 3 ◯ ◯ X ◯ ◯ Com. Ex. 4 ◯ ◯ Δ ◯ X Com. Ex.5 ◯ ◯ Δ ◯ X

As described above in detail, according to the present invention, thereis provided an excellent photoresist stripping solution that causes nocorrosion of Al and Cu wiring conductors or any other metals, hasexcellent strippability for photoresist films and post-ashing residuesand is free from precipitation of a corrosion inhibitor. Use of thephotoresist stripping solution of the present invention makes itpossible to effectively protect both of devices having Al wiringconductors and devices having Cu wiring conductors from corrosion.

1. A photoresist stripping solution which comprises (a) a salt ofhydrofluoric acid with a base free from metal ions, (b) a water-solubleorganic solvent, (c) a mercapto group containing corrosion inhibitor,and (d) water.
 2. The photoresist stripping solution according to claim1, wherein component (a) is ammonium fluoride.
 3. The photoresiststripping solution according to claim 1, wherein component (b) is atleast one member selected from among dimethylformamide,N-methyl-2-pyrrolidone and dimethyl sulfoxide.
 4. The photoresiststripping solution according to claim 1, wherein component (c) is acompound having in its structure a hydroxyl group and/or a carboxylgroup at least one of the α- and β-positions.
 5. The photoresiststripping solution according to claim 1, wherein component (c) is atleast one member selected from among 1-thioglycerol,3-(2-aminophenylthio)-2-hydroxypropylmercaptan,3-(2-hydroxyethylthio)-2-hydroxypropylmercaptan, 2-mercaptopropionicacid and 3-mercaptopropionic acid.
 6. The photoresist stripping solutionaccording to claim 1, which further contains, in addition to components(a)-(d), with the proviso that component (a) is ammonium fluoride, (e) asalt of hydrofluoric acid with a quaternary ammonium hydroxiderepresented by the following general formula (I) and/or an alkanolamine:

wherein r₁, r₂, r₃ and r₄ are each independently an alkyl group or ahydroxyalkyl group having 1 to 4 carbon atoms:
 7. The photoresiststripping solution according to claim 6, wherein the composition ratioof component (a) : component (e) ranges from 2:8 to 8:2 by mass.
 8. Amethod of stripping photoresists which comprises forming a photoresistpattern on a substrate, etching the substrate using said photoresist asa mask, and thereafter stripping away the photoresist pattern from thesubstrate using the photoresist stripping solution according to any oneof claims 1-7.
 9. A method of stripping photoresists which comprisesforming a photoresist pattern on a substrate, etching the substrateusing said photoresist as a mask, then plasma ashing the photoresistpattern, and thereafter stripping away post-plasma ashing residues fromthe substrate using the photoresist stripping solution according to anyone of claims 1-7.
 10. The method of stripping photoresists according toclaim 8, wherein the substrate has either Al wiring conductor or Cuwiring conductor or both thereon.
 11. The method of strippingphotoresists according to claim 8, wherein the substrate has at least anSi-based interlevel film thereof.
 12. The method of strippingphotoresists according to claim 9, wherein the substrate has either Alwiring conductor or Cu wiring conductor or both thereon.
 13. The methodof stripping photoresists according to claim 9, wherein the substratehas at least an Si-based interlevel film thereof.